33. Elastic Solid – Microstructural Behavior ‹ #› The applied force straightens polymer chain segments F F The polymer chain segments return back to a more disorder and stable configuration when force is removed
47. The plastic part is subjected to a tensile force The plastic part is increases its length L, when the force is removed it will not spring back – this a permanent deformation The plastic part is increases its length L F F L o , original length F F L new = L o + L L new = L o + L permanent
50. Viscoelastic Solid, Microstructural Behavior Polymer chain segments are stretched by the force, this is the elastic element of the model As the Polymer chain segments are stretched there is friction between these chain segments – this is the viscous damping element When the force is removed, the chains return to the original state – during this motion, there is also friction Heat is generated
51. General Viscoelastic Model F C E K E C P K E – elastic stretching of chain segments C E – friction between chain segments (very small) C P – friction between complete polymer chains
52. Maxwell Viscoelastic Model F K E C P K E – elastic stretching of chain segments C P – friction between complete polymer chains
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57. time Tension in a part Relaxation curves Increasing temps Initial Tension t o Length after time t o 1 2 3 3 2 1
79. Creep Viscoelastic Model (t) time Critical time For this load, there has not been enough time to start the viscous motion F C E K E Permanent Deformation – creep For this load, the viscous motion has started
93. Small Additives Get between Polymer chains This increases d and can make the degrade properties Example – excess of colorant can weaken a plastic part
99. Melt Flow Index # grams of flow per 10 minutes Weighted Plunger Barrel Molten Pellets Extrudate Orifice Heater Band Dynisco LMI 4000 Len Czuba August 2006